Will alien life be carbon based?

Chris Smith put this question to Cambridge University space scientist Xander Byrne...

Xander - It may not be the only one. People tend to disagree about this a little bit. The one that's often touted as a potential other material that could be useful for this is silicon, right? Because silicon chemically operates quite similarly to carbon in some ways. If you look on a periodic table, silicon is just below carbon. And so chemically they work quite analogously in many cases. The main reason that carbon is so good is because you can make very, very long molecules with it. You can, in theory, have a chain of carbon atoms as long as you like, and you can have a stable molecule as long as it's bounded by lots of other hydrogen atoms and things. But I think for silicon, the longest chain of silicon atoms you can have in a molecule before it starts to break apart a bit is something like 11 atoms of silicon. Beyond that, it's just not a stable molecule. So carbon is really the best for this kind of thing. It's quite difficult to imagine what life could even possibly be like using any other element.

Chris - Does this mean then, Lewis, that if we are looking for life elsewhere across the universe, that probably it will have centred on the same chemical solution that life has here on earth?

Lewis - As astrobiologists, we tend to be focusing on carbon based life or organic based life. Firstly, we know it works. We're good examples of carbon life. But also we're very good at finding carbon based life. We find it in places where it shouldn't be - in hospital surgical theatres or in your bloodstream if you've got an infection. For all the reasons Xander was just saying, we don't think there are viable alternatives to organic chemistry for life as we would know it, but maybe there might be alternatives to water-based life, maybe life on another planet or moon could be ammonia based as it's wet stuff, as it's biosolvent, rather than water. Because ammonia's also pretty good at dissolving lots of different sorts of things.

Chris - So we keep an open mind basically.

Lewis - You try to think outside the box. You don't want to be too blinkered or too focused when you're looking for something which might by definition be alien, be different to how we are.